What this means is that in order to maintain a solid response time of the NuGet service this service has been transferred to Microsoft.
One of the main reasons was the lack of performance for instance in China. My guess is that this is related to the way the Chinese government manages the data infrastructure in China and requires parties to comply to certain regulations. Microsoft obviously has a better position in China to provide services over there.
Keep in mind that NuGet.org is not transferred as a whole, quote:
“The NuGet open source codebase (both the NuGet gallery and the NuGet client) will remain open source and continue as .NET Foundation supported projects under the same terms as before.”
Hopefully we will see an improvement of the NuGet service response times (as said, especially .NET developers in China will benefit significantly) and all will remain to be good.